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% Here is the smodels program
time(0..41).
disk(1..9).

% 41 away 
on0(7,8).
on0(4,7).
on0(1,4). 
on0(2,5). 
on0(6,9). 
on0(3,6). 

% k disks 1,2,...,k. Disks 1, 2, 3 are pegs. Disks 4, 5, ... are "movable"
% The larger the number of the disk, the "smaller" it is.

% Read in data on(T,N,N1) means at time T, disk N1 is on disk N
	on(0,N,N1) :- disk(N;N1), on0(N,N1).
%	:- disk(N;N1), on(0,N,N1), not on0(N,N1).

% Specify valid arrangements of disks
	% Each regular disk is on something
%	1{on(T,N1,N):disk(N1)}1 :- time(T), disk(N), N>=4.
%	:- not on(T,N1,N), time(T), disk(N), N>=4.
%	:- 2{on(T,N1,N):disk(N1)}, time(T), disk(N), N>=4.

	% Basic condition. Smaller disks are on larger ones
	:- time(T), disk(N1;N), on(T,N1,N), N1>=N.

	% disks 1,2,3 are pegs and are not on anything
%	:- time(T), disk(N1;N), on(T,N,N1), N1<=3.

% Specify a valid move (only for T<t)
	% pick a disk to move
	1{move(T,N):disk(N)}1 :- time(T), T<t.

	% pick a disk onto which to move
	1{where(T,N):disk(N)}1 :- time(T), T<t.

	% pegs cannot be moved
	:- time(T), disk(N), T<t, move(T,N), N<=3.

	% only top disk can be moved
	:- time(T), disk(N;N1), T<t, on(T,N,N1), move(T,N).

	% a disk can be placed on top only.
	:- time(T), disk(N;N1), T<t, on(T,N,N1), where(T,N).

	% no disk is moved in two consecutive moves
	:- time(T;T-1), disk(N), T>0, T<t, move(T,N), move(T-1,N).

% Specify effects of a move
	on(T+1,N,N1) :- time(T;T+1), disk(N;N1), T<t, 
	                on(T,N,N1), not move(T,N1).

% T<t, move(T,N), where(T,N1) -> on(T+1,N1,N).
	on(T+1,N1,N) :- time(T), disk(N;N1), T<t, move(T,N), where(T,N1).

% Goal description
        goal :- on(t,8,9), on(t,7,8), on(t,6,7), on(t,5,6), on(t,4,5), 
	        on(t,3,4).
	:- not goal.